Dissolving of nickel-phosphorous alloys



United States Patent "ice DISSOLVING 0F NICKELPHQSIHUROUS ALLUYS Bert J.Sherwood, Los Angeles, and William R. Hoyt, Gardena, Calif., assignorsto Chemplate Corp., Los Angeles, Calif., a corporation of California NoDrawing. Filed Feb. 12, 1957, Ser. No. 639,630

4 Claims. (CI. 75-97) This invention relates to the process of strippingrelatively thin metal coatings from a base metal structure andparticularly to a process and composition for strippingnickel-phosphorous alloy or chemical nickel plating from the metal uponwhich it has been deposited.

Nickel-phosphorous alloy plating or chemical nickel plating is a processwell known in the art for depositing upon ferrous, cuprous, aluminum andcertain other metals and alloys a coating of an alloy having acomposition of from 85 to 99.9 percent nickel and from 0.1 to 15 percentphosphorus without the use of an electrical cur rent. Prior to theadvent of this process, nickel had been plated or deposited byelectrolytic methods and the nickel thus deposited was substantiallypure nickel. To strip the thus conventionally deposited nickel from thesteel specimens or body upon which it had been plated, was accomplishedby a reverse electrolytic process, using sulfuric acid and similarsolutions, by the use of fuming nitric acid as described in US. PatentNo. 2,200,486 or bythe use of an alkaline solution such as suggested inUS. Patent No. 2,649,361. The foregoing three methods for removing orstripping conventional electro-plated nickel however, have been foundunsatisfactory for the stripping or removal of nickel-phosphorous alloyplating inasmuch as the deposit, as noted above, is of a substantiallydifferent composition. The use of the reverse electrolytic processresults in pitting of the base material particularly in the deeprecesses. The other two methods of stripping noted above wereunsuccessful in stripping nickel-phosphorous alloy plating since thedeposited alloy did not respond as electrolytically deposited nickelwould respond and in the first case the solution did not attack thealloy and in the second the alloy was merely made porous.

This invention contemplates a composition which has proved effective inshipping nickel-phosphorous alloy coatings from ferrous and aluminumalloys and a process of using said composition for the successfulstripping of said plating.

It is therefore an object of thisinvention to provide an improvednickel-phosphorous alloy stripping composition.

It is another object of this invention to provide an improvednickel-phosphorous alloy stripping composition which attacksnickel-phosphorous alloy plating but does not attack base metals uponwhich said plating may be deposited such as ferrous alloys and aluminumalloys.

It is another object of this invention to provide an improved method ofstripping nickel-phosphorous alloy plating from the metal upon which ithas been deposited. It is another object of this invention to provide amethod and composition for stripping nickel-phosphorous alloy platingfrom ferrous and aluminum alloys which does not attack or pit the basemetal.

Other objects will become apparent from the following specifications:

The preferred composition of the stripper described in thisinventioaiaamiature 9t acids s i s of t s nitric acid (specific gravity1.49-1.50) 41.5 mole percent and aqueous hydrofluoric acid solution 24.5mole per- 655F511 water 34.0'fiiblpfiiehti lhe stripping is accompli shed by immersion of the nickel-phosphorous alloy plated specimen in theabove mixture at ambient temperature. The time required to strip a giventhickness of nickel-phosphorous alloy plating varies with the relativeconcentrations of the above acids and extremely wide deviations from theabove basic formulation may be made without departing from the scope ofthis invention.

This invention contemplates formulations using nitric acidconcentrations ranging from 72.0 mole percent to 9.0 mole percent andhydrofluoric acid concentrations ranging from 50.3 mole percent to 0.0mole percent and water content ranging from 28.0 mole percent to 58.6mole percent. Formulations composed of acids containing nitrate ions,aqueous acid solutions of fluoride ions or any salt containing thefluoride ion are also considered to be within the scope of thisinvention.

The following examples illustrate the effect of varying the relativeconcentrations of nitric acid and hydrofluoric acid in the abovecompositions:

Example 1 A mixture of 68.4 mole percent nitric acid, 2.9 mole percenthydrofluoric acid and 28.7 mole percent water was placed in a tank linedwith polyethylene in clean and dry condition and a clean, drynickel-phosphorous alloy plated steel specimen was immersed in thesolution. After one and one half hours immersion, the specimen wasremoved, washed, dried and observed to have a light grey metallicappearance of exposed basis metal. A copper sulphate test showedpositive results of complete stripping. Visual inspection under a 3power glass showed no attack of the basis metal. The thickness of thespecimen before immersion was 0.045 inch and after immersion was 0.042inch, indicating that the stripper had removed 1.5 mils ofnickel-phosphorous alloy per side.

Example 2 A steel specimen immersed in a solution of 64.5 mole percentnitric acid, 6.0 mole percent hydrofluoric acid and 29.5 mole percentwater for a period of one hour was completely stripped of its 0.002 inchnickel-phosphorous alloy coating. Tests and inspection described aboveshowed complete plating removal and no attack of the basis metal.

Example 3 The experiments of Examples 1 and 2 were repeated but with59.0 mole percent nitric acid and 10.8 mole percent hydrofluoric acidand 30.2 mole percent water for a period of 30 minutes. The decrease inthickness was observed to be 1.5 mil per side and the specimen wastested and shown to be completely stripped with no visible attack of thebasis metal.

Example 4 In this example the solution consisted of nitric acid 41.5mole percent, hydrofluoric acid, 24.5 mole percent and water, 34.0 molepercent. In a time of 20-25 minutes a decrease in thickness of 1.6 milper side was observed and the above tests revealed complete strippingwithout visible attack to the basis metal. This solution appeared to benear optimum.

In the foregoing it was observed that while solution No. 4 appeared tobe optimum, a fairly wide variation in composition and proportions ofconstituents involved can be tolerated without seriously affecting thequantity of the stripping accomplished. It was observed that it ishighly important that the tanks be lined with inert materials such aspolyethylene and that the parts to be stripped be extremely clean ofgrease, dirt and moisture. Because of the evolution of gas during thechemical stripping, work must be held in such a manner as to permit thegases to escape from any recesses.

Processing of large volumes of work through. the stripping solution willcause an excessive increase in the temperature. For quality stripping,tree of. surface etching, the temperature must be controlled at amaximum of 150 Fahrenheit. No minimum temperature has been establishedas temperature reduction will decrease the stripping rate but in noother way detrimentally afiects the stripping efficiency. I Although theinvention has been described and illustrated in detail, the same is tobe understood to be by way' of illustration and example only, the spiritand scope of the invention being limited only by the terms of theappended claims.

We claim:

1. The method of stripping nickel-phosphorous alloy plating from a steelworkpiece without attacking the base metal, including the step of:immersing the workpiece in a stripping bath containing from about 41.5mole percent to about 68.4 mole percent fuming nitric acid, from about2.9 mole percent to about 24.5 mole percent hydrofluoric acid, and theremainder water.

2. The method of stripping nickel-phosphorous alloy plating from a steelworkpiece without attacking the base metal, including the step of:immersing the workpiece in a stripping bath containing about 41.5 molepercent 4 fuming nitric acid, about 24.5 mole percent hydrofluoric acid,and the remainder water.

3. The method of stripping nickel-phosphorous alloy plating from a steelworkpiece without attacking the base metal, including the step of:immersing the workpiece in a stripping bath maintained at a temperatureno greater than about Fahrenheit and containing from about 4L5 molepercent to about 68.4 mole percent fuming nitric acid, from about 2.9mole percent to about 24.5 mole percent hydrofluoric acid, and theremainder water.

4. The method of stripping nickel-phosphorous alloy plating from a steelworkpiece without attacking the base metal, including the step of:immersing the workpiece in a stripping bath maintained at a temperatureno greater than about 150 Fahrenheit and containing about 41.5 molepercent fuming nitric acid, about 24.5 mole percent hydrofluoric acid,and the remainder water.

References Cited in the file of this patent UNITED STATES PATENTS1,974,570 Kiefer Sept. 25, 1934 2,200,486 Burdick May 14, 1940 2,371,529Loose Mar. 13, 1945 2,541,083 McDermotte Feb. 13, 1951 2,564,749 BriedAug. 21, 1951 2,569,158 Francis Sept. 25, 1951 2,740,700 Fuller Apr. 3,1956 FOREIGN PATENTS 503,304 Canada May 25, 1954 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No, 2 954 289 September 27 196Bert J. Sherwood e1; alt,

It is hereby certified that error appears in the-printed specificatio ofthe above numbered patent requiring correction and that the said LetterPatent should read as corrected below.

Column 2 line 71 for "quantity" read quality a Signed and sealed this11th day of April 1961 (SEAL) Att t: sR l lEsT w. SWIDER ARTHUR W.CROCKER Attesting Oflicer Actmg Commissioner of Patents

1. THE METHOD OF STRIPPING NICKEL-PHOSPHOROUS ALLOY PLATING FROM A STEELWORKPIECE WITHOUT ATTACKING THE BASE METAL, INCLUDING THE STEP OF:IMMERSING THE WORKPIECE IN A STRIPPING BATH CONTAINING FROM ABOUT 41.5MOLE PERCENT TO ABOUT 68.4 MOLE PERCENT FUMING NITRIC ACID, FROM ABOUT2.9 MOLE PERCENT TO ABOUT 24.5 MOLE PERCENT HYDROFLUORIC ACID, AND THEREMAINDER WATER.